program exam1;
function ismonth (X:integer):boolean;
begin
if (X>0) and (X<13) then ismonth:=true
else ismonth:=false;
end;
begin
writeln('month 4: ',ismonth(4));
writeln('month 31: ',ismonth(31));
readln();
end.

-----------------------or-----------------------

program exam1;
function ismonth (X:integer):boolean;
begin
if (X>=1) and (X<=12) then ismonth:=true
else ismonth:=false;
end;
var month:integer;
begin
writeln('Enter a various MONTH');
readln(month);
writeln('Is it a valid month? ',ismonth(month));
readln();
end.